1. Field of the Invention
The present invention relates to a flashback-detecting equipment and a flashback-detecting method which detect a flashback occurring during combustion of a combustor, and especially, relates to a flashback-detecting equipment and a flashback-detecting method which detect a flashback in a combustor being cooled by a cooling fluid.
2. Description of the Prior Art
In recent years, in order to reduce air pollution, at electric generation facilities utilizing gas turbines, it is demanded to reduce NOx being included in exhaust gas thereof. NOx in a gas turbine is generated in a combustor which performs combustion in order to rotate a gas turbine. Therefore, conventionally, in order to reduce NOx being generated in a combustor, is employed a combustor being provided with main nozzles that perform combustion (premixed combustion) by mixing a fuel with the air.
By having the main nozzles perform premixed combustion, it is possible to reduce the amount of NOx being exhausted from the combustor. However, combustion state thereof is unstable, and combustion vibrations occur. Therefore, in order to restrain the combustion vibrations so as to make the combustion state stable, such a combustor is employed as is further equipped with a pilot nozzle which diffuses and burns a fuel (diffusion combustion). FIG. 5 shows a schematic block diagram of a combustor being provided with a pilot nozzle and main nozzles as described hereinabove.
Around a pilot nozzle 101 being provided with a cone for forming a diffusion flame by having the pilot fuel and combustion air react, a combustor in FIG. 5 is provided with a plurality of main nozzles 102 producing and injecting a pre-mixture gas of a main fuel and combustion air so as to generate a premixed flame. Then, the combustor in FIG. 5 comprises a combustor basket 103 having a pilot nozzle 101 and main nozzles 102 inserted therein and a transition piece 104 which has the combustor basket inserted therein and discharges combustion gas. By being provided with the main nozzles 102 in this manner, combustion of pre-mixture gas controls the combustion temperature so as to heat the combustion gas being discharged from the transition piece 104 up to high temperature. In order to deal with heating of the combustion gas to attain high temperature, the present applicant provided a combustor being equipped with a cooling structure that cools the transition piece with cooling steam. (See the Japanese Patent Applications Laid-Open No. 2001-263092.)
However, in premixed combustion burning a gaseous pre-mixture, a range of stable combustion is narrow, and by a change in flow rate and fluctuation of fuel-air ratio due to an increase or a decrease in flow volume of the gaseous pre-mixture, a location where the premixed flame is formed is shifted to upstream side, thereby generating a flashback phenomenon. In order to detect a flashback, there is a flashback-detecting sensor which detects a flashback by detecting an outlet temperature of a combustor. However, because combustion gas being discharged is heated to high temperature, an available location to install a flashback-detecting sensor is limited. In addition, even though each sensor serving as a flashback sensor is installed to the limited location, it is difficult to detect a flashback properly because each sensor does not directly detect a flashback.